(1) Field of the Invention
The present invention relates to charging devices for shaft furnaces which have a fixed feed channel positioned vertically in the centre of the furnace head. More particularly, this invention is directed to charging devices including a rotary ferrule mounted coaxially around the said feed channel, a substantially cylindrical fixed wall mounted coaxially outside the said ferrule, in conjunction with which it laterally and internally delimits a substantially cylindrical and annular chamber, this chamber being separated but not isolated from the interior of the furnace by means of an annular disc integral with the rotary ferrule, a distribution spout pivotably mounted at the base of the rotary ferrule, a control rod articulated to the spout and penetrating the said chamber via the annular disc, a first driving means serving to cause the ferrule, annular disc, spout and control rod as to rotate as one assembly around the vertical axis of the furnace and of the feed channel, and a second driving means serving to pivot the spout by means of the control rod, independently of the movement resulting from the action of the first driving means, around the horizontal shaft by which it is suspended from the ferrule.
(2) Description of the Prior Art
Furnace charging devices with a rotary spout or chute of which the pouring angle is adjustable are at present well known in the branch of industry concerned. The success of charging systems employing such rotatable and angularly adjustable distribution chutes is due firstly to the fact that they have made it possible to surpass the operating limits already achieved some time previously with the conventional bell-type charging devices and secondly to the fact that such systems enable the charging operation and therefore the actual operation of the furnace to be controlled more satisfactorily.
The movement i.e., the aiming, of the spout is generally brought about through the use of by two separate motors. The output shaft rotation of these motors is converted into rotary and pivotal spout motion by recourse to contrivances based on the use of wheels and gearings, particularly those performing differential and planetary movements. These driving mechanisms are required to be capable of guiding the spout to aim the charge material, which falls under the influence of gravity, to any arbitrary point on the charging surface and of enabling the material to be deposited in clearly defined configurations capable of contributing to the optimization of the furnace operation.
The numerous charging devices of this type essentially fall into two categories, according to the mechanism used for adjusting the pouring angle of the spout. The first type is based on the use of a control rod articulated to the spout and caused to perform an ascending or descending movement in order to pivot the spout around its horizontal suspension shafts, while in a second type of charging device the horizontal suspension shaft of the spout are itself caused to perform rotary movements.
The devices included in the first of the above-mentioned categories, is exemplified by the disclosure of U.S. Pat. No. 3,864,984 and British Pat. No. 1,322,798. Among the advantages offered by devices of the type disclosed in the above-mentioned U.S. patent is the relatively moderate width of the annular chamber in which the control rod moves. Among the major drawbacks of this type device is of the comparatively complex mechanisms required for the purpose of superimposing on the gyratory movement of the control rod, around the admission chamber, a vertical translatory movement serving to set up the pivoting motion of the spout in relation to the vertical axis. It should further be noted that while numerous mechanisms of the general type disclosed in U.S. Pat. No. 3,864,984 have been proposed, either in technical articles or in patents or patent applications, no device of this kind has so far been actually constructed and employed, the experts in this branch of industry having placed more confidence in those of the second category discussed.
An example of steerable charging devices of the second category, i.e., devices wherein the angular spout adjustment is achieved through rotation of the horizontal suspension shafts of the spout, is described in detail in the British Patent specification 1403687. In devices of the type described in this British patent the operation of adjusting the pouring angle of the spout is performed by means of two gear boxes positioned symmetrically, at the two ends of the spout suspension shaft, in the annular chamber around the vertical feed channel, the gear boxes gravitating about the feed channel. Charging devices of this type have been actually put into operation in numerous blast furnaces, particulary those of the modern high-capacity type. Among the points to be mentioned in favour of this type of device is the fact that all the movements are generated and transmitted by gearings, i.e. efficient, simple and reliable means, of which the forces are applied to the spout symmetrically. However, the need for two gear boxes gravitating around the feed channel necessarily increases the width of the annular chamber in which the gear boxes move and also increases the width of the annular disc separating the feed channel from the interior of the furnace. In other words, the surface exposed to the temperature prevailing in the furnace has an ample area, necessitating additional cooling for the annular chamber and for the driving devices housed therein, such cooling being achieved by the circulation of cooled inert gas. While the advantages of charging devices of the type being discussed justify installation of such devices in modern high-performance blast furnaces, the cost and the auxiliary equipment required render the use of these controllable charging devices less advantageous in the case of furnaces of medium and low capacity.